I'm trying to bring up the MCU on the board, but I cannot get an accurate or consistent MCU ID out of the chips. So, I'm set aside that struggle for later. Just swapped in a 328PB from an Arduino Uno, and it's alive and well at 16 MHz! RGB LED responds correctly, and the serial port is spewing data.

I've been able to burn a boot loader to a Pololu A-Star 328PB with the AVR ISP mkII, but I'm missing something with the fresh 328PB's I bought from Digi-Key. Since a swapped in 328PB works fine, I think the basic circuit and connections are in good shape. I'm not going to try and re-burn the boot loader in the 328PB I swapped in now... maybe later. I will try to program the new 328PB's in the Arduino Uno later on though.

On to bringing up the I2C and SAO port with OLED next.